1. Field of the Invention
The present invention relates to an optical apparatus arranged to move an optical member, such as a lens.
2. Description of the Related Art
The optical apparatus shown in FIGS. 6 and 7 includes a first lens holding member 101 which holds a first lens group I, a second lens holding member 102 which holds a second lens group II, a third lens holding member 103 which holds a third lens group III, and a fourth lens holding member 104 which holds a fourth lens group IV. The first lens group I and the third lens group III are fixed lens groups, the second lens group II is a moving lens group for performing a zooming action, and the fourth lens group IV is a moving lens group for performing a focusing action. The second lens holding member 102 is held for sliding movement along the optical axis by guide levers 105 and 106 each of which is supported at one end by the first lens holding member 101 and at the other end by the third lens holding member 103. A rack member 107 supported by the second lens holding member 102 meshes with a screw shaft 108a of an arc-shaped zooming motor 108 fixed to the third lens holding member 103, so that the second lens holding member 102 moves along the optical axis by the rotation of the screw shaft 108a of the zooming motor 108. The forward end of the screw shaft 108a is rotatably supported by a bearing 109 which is provided on the first lens holding member 101.
The first lens holding member 101 has an opening 101a which is covered with a cover 110. The opening 101a is provided for aiding in incorporating the screw shaft 108a into the first lens holding member 101 to mesh the screw shaft 108a with the rack member 107 and for allowing a visual inspection of the inside of the first lens holding member 101. The fourth lens holding member 104 is supported for movement along the optical axis by second guide bars 112 and 113 each of which is supported at one end by the third lens holding member 103 and at the other end by a rear fixed lens barrel 111 having an image-pickup-element mounting part 111b (FIG. 7).
Referring to FIG. 7, a rack member 114 supported by the fourth lens holding member 104 meshes with a screw shaft 115a of an arc-shaped focusing motor 115 fixed to the rear fixed lens barrel 111. The fourth lens holding member 104 moves along the optical axis by the rotation of the focusing motor 115. Similarly to the screw shaft 108a of the zooming motor 108, the forward end of the screw shaft 115a is rotatably supported by a bearing (not shown) provided on the rear fixed lens barrel 111, and an opening (not shown) for aiding in performing incorporating work and visual inspection, which is provided in the rear fixed lens barrel 111, is covered with a cover 116.
The arrangement shown in FIGS. 6 and 7 also includes iris blades 117 and 118, and an ND filter 119 (not shown in FIG. 6) is attached to the iris blade 118. The iris blades 117 and 118 are retained between a blade pressure plate 120 and the third lens holding member 103, and are driven by the swinging motion of a driving arm 121a of an arc-shaped iris driving part 121.
However, the above-described example involves a lowering in space factor and increases the size of a lens driving device, because it is necessary to use rotating motors, such as stepping motors, and transmission members, such as rack members, for converting the rotational motions of the corresponding rotating motors into rectilinear motions.
Another consideration is that such a rack member or the like may come off on account of an accident such as a fall or a shock to disable the movement of a lens holding member.
As described above, the lens holding member normally has a single guide hole and a single guide groove, and is capable of moving along the optical axis by means of two guide members one of which is inserted through the single guide hole and the other of which is fitted in the single guide groove. Yet another consideration is, therefore, that since a play is normally present between either of the guide members and the guide hole or the guide groove, the eccentricity or the like of the lead screw shaft of a motor may disable the lens holding member from moving along the optical axis with high precision and may also cause an image-waver phenomenon or the like.
The arrangement of a position detecting part of a movable lens holding member of the type described in Japanese Laid-Open Patent Application No. Hei 3-251830, Hei 4-93907 or the like is such that the movable lens holding member is connected to a potentiometer or the like disposed outside a lens barrel by a connecting member. Yet another consideration is, therefore, that highly precise position detection may not be performed owing to a play between a lens frame and a guide pole fitted into the lens frame and a play between the lens frame and the connecting member which connects the lens frame to a detector such as the potentiometer.
A further consideration is that, in the case of the arrangement of the position detector described in Japanese Laid-Open Patent Application No. Hei 5-328696 or the like, the gap between a position detecting magnet and a detector may not be maintained at a constant distance owing to a play between a moving element and a guide shaft and highly precise position detection may not be performed.